Interference elimination system



April 23, 1935. J. SEDLMAYER INTERFERENCE ELIMINATION SYSTEM Filed May17, 1934 INVENTOR JOSEPH SEDLMAYER E #QQ Aff-wu..

ATTORNEY n Y Patented Apr. 23, 1935 UNITED -sTME-s insana 1,998,792 YvnrrEnFEaranci.: ELIMINATION SYSTEMl Application May'ir, 1934, serialNo. 726,038 Y f y i .Inv Germany April 12, 1933 2 Claims.

The present invention relates to a'method of and means for eliminatinginterference in the .1 electric signal communication systemswhereinmessages are transmitted by means of impulse 5 signals, as forexample, in alternating current telegraphy. It is suitable for thetransmission over wires as well as over Wireless paths. [The advantagederived from the invention lies in the;

fact that interferences of the most various types are caught and removedsimultaneously with the result that an actually reliable transmissionlof messages is. guaranteed.

It is known in the field of Wireless communication, particularly in theshort-Wave art, that interference phenomena exist in the form ofslelective fadings which make their existence known by the variation ofthe intensity only of a part of the frequencies of a transmittedfrequency band. Attempts have heretofore been made to 2O eliminate theinfluence of fading on this type by emitting simultaneously, ormodulating upona joint carrierr wave several frequencies, for in-rstance a fundamental Wave and harmonicwaves of the same frequency. Thenagain, there are interferences which produce additional currents in thereceiving apparatus and which. for in'-VV stance in Wirelesstransmission, are caused by atmospheric influences. For thepurposeofreliable reception for this case, the prior art has proposed the useof ,-a so-called double tonal control, i. e. to sendv one frequency forthe signal current vand another frequency for the spacing current. Insuch case there is provided at the receiving end a differential circuitscheme which operates the receiving apparatus with, the alternatingreception of the two frequencies. Thus the interferences arepovverlessfin that the frequencies used for signal transmission arecontained therein which influencesimuLl taneously both parts of thedifferential circuit 'so that the receiving apparatus is not actuated.In the. transmission by Wire, interferences may appear in similarmanner, for instances interfering impulses by adjacent linesorpby for- Veign sources of disturbances maybe produced, or the transmissioncharacteristics'may be teinporarily changed for certain frequencies by-aswitch-over, for example in high tensionv lines.`

According to the present invention, the above listed phenomena whichcause interference are eliminated for the same transmission channel bycombining with each other the two methods described. In other words, useis made of double tonal control and of severalfrequencies which are'preferably in harmonic relationship, for each the signal current'andthe spacing current. Moreover, in addition, there is proposed accordingto the invention a new arrangement for the elimination ofthe itotalfading, i. e., suchffadings'which do not favor special frequencies butwhich cause a, uniformfading of the sound intensity. This isaccomplished by connecting level regulating arrangements` in thosebranches in receiving circuits whichare separated for the purpose of theeliminationpof interferences and which act, for'instance with respect tothe interferences, in opposition toea'chother orwhich, wheninterferenceoccurs, carry different-parts of the incoming. energy andact integrating on WVEMF OFFICE the'receiving apparatus.` `It is furthersuitable i for.- the .purpose of providing a yfurther-'joint coarseregulation in'the`joint part of the input of the receivingv arrangement.The advantages derivedtherefrom consist, inthe `first place, in-

purging the currents fed to the regulating amplifiers of interferencesto an appreciable. degree' so thatthes'e latterrcan v*no longer exert anotice-y able inuence on thev adjusting apparatuscontained in thebranches` Invithe second place, an advantage must be seen in the factthat with the use of a coarse regulation the adjusting range of theregulators contained in the branches can be kept considerably smallerthan Without the use of' a coarse'adjuste'r. ...Thus'the required inputcan beheld down considerably. By a coupling ofthe'controls Ycontained inthe branches the elimination of total fading can be further effected byboth regulators jointly, the one of the selectivefading by the', one orthe other regulator Whichis in the branchwherein the selective fadingfalls. In this manner the regulators in the different branches may bekept approximately at the same level during the transmission, the

additional vernier regulation taking place separately in each branch. l

Further. details of the invention are explained by means of theaccompanying drawing, which is given vbyiw'ayofiexample: i

Fig. l shows'the frequency scheme of an arrangement according totheinvention.l Fig. 2 represents aschematic diagram of the circuitarrangement according to Fig. l.

Fig. 3 shows closerv details "of the receiving ar y rangementaccording'to Fig. 2. f V-The circuitembodiment shown by Way of eX- ampleisfintended for the transmission of telegraphic signals,'wherein alsocurrents are trans? mitted during the signal spaces which have afrequency different from those of thesignal currents, in other words,use is made of a so-called doubletonal control vAccording to Fig. l thecarrier frequency fais modulated during the signal current period with afrequency f1 and its first harmonic'frequency 2jr Vand during thespacing period with a frequency f2 and its rst harmonic 212. Hence,besidethe carrier frequency ft there are sent duringV the signal theside frequenciesA fil-f1 ,and ftiZfi and during .the spacing the side o'frequencies ftifz and fri-U2. Thechange'between the two frequency pairsf1, 2h and f1, 2fg corresponds to a frequency modulation. Thecorresponding frequencies of both frequency pairs must be diiferent fromeach other only so inuch that a sufficient separation by filter can beef fected. Let it be assumed for instance that the frequencies f1 and 2haccording to Fig. l are i090 Hertz and 2000 Hertz and the frequencies f2and f2 i200 liertz and 2400 Herts.r

f he combination of side band frequencies having harmonic relationshippractically removes the influence of the carrier Wave fading. With theabsence of the carrier frequency, therev arepro" duced afterrectification at the receiving end, frorn the side bands only, thetransmitted fundamental frequencies and their upper harmonics, forinstance according to Fig. l the frequencies fr, 2f1, 311, and f1 andf2, fz, Biz and'fz, respectively. Compared with the standardtransmission, only the amplitude of the individual frequencies thenchange. Since this amplitude variation can be balanced'by fadingregulation, it is possible to practically eliminate the influencefof thecarrier wave fading. in order to bring to practical reali-V cation thebasic idea of the invention, use could be rnade in place of afundamental frequency and its first upper harmonic' also of afundamental frequency and several harmonics, or only ofthe latter alone.It may even be advantageous to employ only frequencies having somehow orother positive relationship with a fundamental frequency andtodifferentiate signal current and spacing current by variation of thefundamental frequency.

According to Fig. 2 there is arranged at the sending side (left) agenerator G which produces with opened contact of thel sending relaySi?,l 1280 l-lertz and with closed contact 1000 Hertz by the addition ofa capacityC. Letthe last-.named freu quency. correspond to the signalcurrent. The harmonics ofV the said fundamental frequency are producedby distortion in a strongly biased discharge tube VZ. The net system Nserves to filter out the fundamental frequency and the first harmonicand torequalize or make even the amplitudes of both frequencies. Thefrequencies are then amplified in an amplifier V andmodulated onto thecarrier frequency (fr in Fig. l) in the modulator M. The carrierfrequency is a'nplified in the emitting amplierS and radif ated from thetransmitting antenna SA.

At the receiving end the carrier frequency'is received by the receivingantenna EA and demodulated in receiver E. Connected to receiver E is acoarse regulator RG. The produced inodulation frequencies whichcorrespond to the froquencies produced at the sending end by generatorG- or disto-rter VZ respectively are'then filtered through four bandfilters. The outlets of the band filter for 1000 and 2000 Hertz lead toa branch V1 of the adjusting amplifier RV, the outlets of the filtersfor i200 and 2460 Hertz to a branch V The adjusting amplifier has threestages or steps of which the last is arranged as rectifier. at Vtheoutlet of the rectifier step is disposed the receiving relay ER indifferential cir cuit arrangement in such manner that interfer-- enceamplitudes arriving simultaneously in the signal and spacing currentchannel do not bring the relay to response.

The two adjusting amplifiers low frequency channels V1, V2 arepresuniedto 'have such a relationship to each other that the regulatorV2 disposed in the spacing channelis entra-ined by regulator andoperates in the disposed in the sarne` sense vwhen the latter respondsand vice versa. This coupling has the following purpose: If it isdesired that all distortions which the signal undergoes duringtransmission should be compensated to the most possible degree, theduration of adjustment of each regulator must not exceed the duration ofan elementary signal even for the maximum occurring level variations.

. If the regulators were independent of each other,

the result would be that the regulator disposed in the non-'used channelat that particular moment would respond, bringing the distortion level,alone present in its inlet, to the theoretical value proscribed for thesignal. In this manner, theI distance between used level (in the usedchannel) and distortion level (in the unused channel) would be-,so muchshorter as toA interfere with a reliable Working of the differentialrelay. In accordance with the invention the regulator clisposed in theusedy cl'rannnell shifts with the response at the saine time as the gridbiasing potential of the regulator in the unused channel to such adegree that the latter cannot be made to respond at all from theAdistortion level alone. This locking is only released when the usefulamplitude drops in the first regulator and when it jumps over the secondchannel Whose regulator now again locks the first. The regulation of thetotal fading is done by both regulators jointly and the one .of theselective fading by the regulators individually, both regulators beingapproximately at the saine level during the transmission, only theadditional fine regulation taking place individually in each channel.

The .arrangement of a coarse regulator RG further accomplishes that thetotal level which is fed to the band filters Bf, has already experienceda certain regulation. Such a'coarse regulation assures a smallerregulation range of the regulators disposed in the branch channels,considerably smaller than in the case where the Vernier regulators hadto take up the entire regulating task. The necessary input can thereforebe kept in closer limits. lt is not essential whether the coarseregulator is arranged before or behind the demodulator and care inustonly be taken regarding its dirnensioning that jumpy variations of thearriving held intensity are regulated during time period which is.srnall ccrnpared to the time period of an elementary signal.

The band filters Bf must be diinensioned so that the alternatingcurrents fed to the regulation amplifiers V1, V2 are already sharplyltered out. The action of additional interference impulses with respectof regulation amplifiers V1, V2 is greatly lessened by means of such anarrangement. Y

Fig. 3 shows an exemplified embodiment of the regulating amplifier setsVI V2 being coupled with each other. The amplifier V! comprises the twoseries-connected amplifier tubes RVi, RVZ and the rectifier tube Gl; andthe amplifier V 2 similarly comprises the tubes RVi', RVZ and Gi. Theoutputs of the band-pass filters B'l, designed for l000'and 2000 cps(corresponding to signal current), are united by Way of the inputtransformers U1 with the grid circuit of tube RVi, and the band-passfilters Effi, designed for the frequencies 1200 and 2400 cps, areirnilarly associated by Way of the transformer U1 with the grid of thetub-e RVi. In the grid circuit of each of the'two tif-.bes is .includned a capacity resistance circuit scheine CI, Rl, and CI', Ri',respectively, by which, upon the arising of grid current, there isoccasioned a displacement voltage as a function of the amplitude orstrength of the incoming current impulses. For instance, as soon as asignal current comes in, that is to say, as soon as currents flowthrough the band-pass lters Bfl, Bf2, there flows also a grid current inthe tube RVI which causes a fall of potential across the resistance RIsuch that the tube becomes negatively biased. In other words, theWorking point is shifted towards the lower knee. The stronger thecurrents flowing through Bfl, Bf2, the more will the Working point ofthe tube RV! beshifted downwardsand the lower will become the gain ofthe tube RVI. However, inasmuch as the amplitude of the grid voltagewill grow at the sametime, conditions may be so made that,`if a state ofproper balance or adaptationis created, the amplitude by and large willvbe fairly stabilized at the output end of the tube RVH. VThe output ofthe latter tube is in inductive coupling relationship with the amplifiertube RV2, While the output circuit of thislast-named tube, in turn, isinductively coupled with the rectier tube GI. In the grid circuits ofthe tubes RVZ and Gi are included the same stabilizing arrangements asin the grid circuit of the tube RVi, i. e., C2, R2, and C3,'R3,respectively. As a result of this cascade arrange; nient of theregulator means, the sensitiveness `of the regulatory action or thedegree of constancy of the output amplitude, is enhanced toV anextraordinary extent. The same thing holds good for the tubes RV! RV2,Gl 'Y of the ampliiier end V2. In fact, the grid circuits thereofcontain corresponding regulatingk means denoted by CI',

Rl', and C2', R2', and C3', R3.

The grid circuits of the tubes RVI, RVi', and RV2, RVE', respectivelyVare, in addition, coupled leach by a resistance WI and AW2,respectively, with the result. that the regulation of the tubes RVi,

RVi', and RV2, RVZ is rendered independent of each other. Thisindependence consists in that whenever an impulse current iiows throughone end Vi or V2, the'respective other branch or end V2 or Vl, as thecase may be, is blocked for the passage of an impulse'. For instance, ifcurrent iiows through the band-pass filters Bfl, Bf, the grid currentabove referred to also causes, by way of Rl, a fall of potential acrossWI, and this occasions, at the grid of tube RVi a negative biasingvoltage so that by interference or stray currents liable to reach thegrid of the tube RVi by way of the bandpass lters Bf, Bf4, prac-Ytically no current will be caused to iiow inthe plate circuit of thetube BVI. A choke capacity arrangement DI, Kl, and D! KI is arranged'inparallel relation to the resistanceWl.l The capacities Kl, Ki' serve thepurpose of short-circuiting the resistance W l for the currents comingfrom the band-pass filters in order that thecurrents operative at thegrid of one of the'tubes RVI or RV! by way of the coupling throughresistance W may not, at the same time, be able to reach the grid of therespective other tube RVI or RVi This short-circuiting action isincreased and'promoted by the aid of the choke-coils Dl, Di these latterbeing so dimensioned (voltage division) that, of the voltagearisingacross the terminals of the capacities Kl and Kl only a small portionwill be able to become active across the resistance I Wi. The same thingholds true of the tubes RV2, RVZ (V72, D2, K2, and W2", D2', KZ).

The choke capacity schemesV AI, Cl I, and A2, C22,^and AI', CI', andA2', C22', respectively,

serve, as known from the prior art, for the purpose of precluding theplate alternating current from the plate supply battery and ofpreventing coupling of the tubes with one another by way of the platesupply. The grid voltage of the rectiized by a circuit arrangement ashereinbefore disclosed is that, as long as one of the amplier branchesor ends is traversed by an impulse, the respective other amplier branchis non-transmissive. To be sure, this inter-dependence is obtainablealso by thevuse of other suitable Ways and means, say by the couplingVthrough resistancesWl, W2, etc., or by coupling through suitable tubearrangements. It is also feasible that instead of filter schemes DI, Kl,etc., multi-mesh chains or networks aroused. The time constants of theregulator circuits Ci, Rl ,and Ci Rl may'V moreover bedetermined andiixed independently vof the time constants of the' coupling means WL DI,KI, DI', Kl.

I claim.

f 1. In a radiortelegraph system, the method of eliminating interferencein communication which comprises modulating a high frequency carrierfrequency by an audio frequencyvcurrent and its rst harmonic during asignalling period, modulating the same carrier by a different audiofre-- quency current and its first harmonic during the spacing period,radiating Vthe resultant energy,

receiving the energy and selectivelyseparating out the two Vaudiofrequencies and their respectivefi-l'rst harmonics, passing one audiofrequency f current and its first harmonic through one path and vtheother audio frequency current and its .first harmonic through anotherpath, and differ-v entially recording the passage of Asaid energythrough said two paths. n

2. A telegraph system comprising, in combination, a signal relay havingtwo positions of operation, an oscillation generator responsive to oneposition of said relay toA generate one fre-v quency and to the otherposition of said relay to generate -anotherrfrequency a'distortingdevice in circuit with the output-of said generator producing a harmonicof bo-th said frequencies, a filter connected to said distorting devicefor eni abling the passage therethrough of said two frequencies andtheir harmonics, van amplifier for amplifying said two frequencies andtheir harmonics, means for modulating a carrier wave by said twofrequencies and their harmonics and forv transmitting same, a receiverhaving filters for separately ltering out and passing said twofrequencies and their respective harmonics, a differential relay havingtwo windings, means for applying one of said filtered frequencies anditsY harmonic to one of said windings and the other frequency and itsharmonic to the other winding,

whereby interfering currents received by said receiver affect bothwindings of said relay equally l and in opposite sense. Y JOSEPHSEDLMAYER.

